I seem to recall that Rick Willoughby offered some hull and rocker alternatives a while ago for Dennis' design in which a bit of "planing" surface forward and/or suction effects aft would help counteract bow-down trim in the speed range of interest, modeled via Leo Lazuaskas' MIchlet/Godzilla suite.
Question: what are the scaling effects for hull and sail surfaces when testing physical models in real-world full-scale winds (which I suspect had outsize effects for Todd's models)? I suspect there are varied Reynolds number factors involved, possibly different for the water and air foils.
...and whatever happened to Dennis' project?
Mike
On Mar 9, 2011, at 4:49 PM, Rob Denney wrote:
> Rudolph,
> Did it sail bow down with the old rudders? Was there any noticable
> change in trim with the front rudder raised? Did it make any
> difference upwind or down? Do the new rudders steer ok downwind?
> Sorry about all the questions, but the more I know, the more able I am
> to sort it out.
>
> Ben,
> There is no question it is sailing bow down and no doubt this affects
> the steering. The question is why is it bow down? I suspect it is
> because the rudders are turned at a big angle. The only other change
> is the keel. If it is the rudder angle, the next question is why are
> they at such an angle? Obviously a clr/coe balance problem. But if
> you lift the front one (or align it with the flow), the coe is ahead
> of the clr of the aft rudder which should provide lee helm. The keel
> will influence this, not sure how much. If you reduce the sail area
> aft of the coe (reef the main, the lee helm should be even more
> pronounced. Apparently (Rudolph?) it wasn't.
>
> I have found that once any of the boats are moving, the helm is pretty
> easy (see the various videos). BD is the exception to this. The
> time when it can be tricky to steer is coming out of a shunt. That is
> when big rudders and no fixed foils work best, in my experience.
>
> All very perplexing.
>
> rob
>
>
> On Tue, Mar 8, 2011 at 6:03 PM, Rudolf vd Brug <rpvdb@freeler.nl> wrote:
>> Hi,
>>
>>> Forgetting the draft requirement, do you thhink they would have worked
>>> better if they were the same size, or even slightly larger than the
>>> originals?
>>
>> Comparing the two systems the old rudders being wider apart was clearly
>> better.
>> The area of the old rudders seemed generous. We sailed with rudders
>> partially raised which didn't change the feel much if any.
>> Front rudder up or down, no difference.
>> That is why I think extra area on the new ones wouldn't make much
>> difference. If it's not working with a bit less area it's not
>> good enough. That may be the present situation (less area that is).
>>
>> Maybe the effect of the keel is simply that it keeps CLA closer to the
>> centre than without one in bow down trim.
>>
>> Rudolf
>>
>>
>>
>> ------------------------------------
>>
>> Yahoo!7 Groups Links
>>
>>
>>
>>
>
>
> ------------------------------------
>
> Yahoo!7 Groups Links
>
>
>
>